In 1859, On the Origin of Species introduced Charles Darwin’s theory of evolution to the world. Although theories of evolution were already widespread, Darwin’s mechanism of natural selection offered a novel explanation of how evolution occurred. The book provoked an immediate and widespread reaction. Many Christians, notably the botanist Asa Gray, believed that Darwin’s theories were compatible with the Christian faith, while others argued evolution contradicted the biblical account of creation. This is the third print run of the first American edition, which appeared in 1860. Although the word “Revised” was added to the title page of the third print run, the text is identical to the first two print runs, all of which follow the first 1859 English edition.